MODULATION TECHNIQUES FOR CABLE TELEVISION DISTRIBUTION ON OPTICAL FIBRES.

Modulation techniques are compared for local cable television distribution on optical fibers. The comparison is based on the allowable fiber loss for a given unweighted snr and transmission bandwidth. A general form of expression is obtained for the snr of seven modulation techniques. Pulse width modulation and pulse frequency modulation, both with direct baseband recovery of the analog video signals, are shown to achieve similar allowable losses as analog intensity modulation for the same transmission bandwidth. At the expense of increased bandwidth, frequency modulation offers a larger allowable loss, especially with pre-emphasis of the video signal. Pulse code modulation has the best performance, but with a significant increase in circuit complexity compared with the other techniques. The choice of a modulation technique depends on many factors and no one technique is concluded to be a clear candidate.